What had been a picture-perfect Sunday afternoon at Horseneck Beach, digging in the sand with his young sons, 5 and 7, quickly changed direction with a phone call from the city’s animal control officers.

That day there had been sitings by motorists of an alligator along grassy sections of the South End near the highway, and when Schenck showed up about 4:30 p.m., he knew what to expect.

In what looked liked “an old-fashioned drainage ditch,” perhaps 4 feet deep, the dark green alligator “was floating, looking right at everybody.” He said it was a young female, estimated its size at 5 to 6 feet long and 50 pounds.

Schenck knew it was an alligator, not the nastier crocodile, by its short snout and single row of teeth, he said.

He said alligators are illegal as pets in Massachusetts, but not in Rhode Island.

With his kids watching from the car, he quickly ventured into the swampy area near Routes 24 and 81 and the Harbour Mall.

Armed only with a roll of electrical tape, the owner of Animal Instincts at 811 Plymouth Ave. for the past 18 years and a lifelong animal lover said he’d handled large reptiles, including alligators, “hundreds of times.”

“I grabbed her behind the head and the base of her tail to prevent her from rolling,” Schenck said.

The chunky alligator, he said, “was in phenomenal shape” judging by the fat in the base of the tail. State officials would later confirm that.

He secured her mouth shut with several layers of black tape. Carrying her out of the wide ditch, both man and reptile emerged covered with leaches the size of half-dollars, he said. He took about a dozen off her belly.

This was the second time in a couple of weeks Schenck has taken part in a search-and-rescue mission for a runaway reptile. In one of his tanks, he’s nursed a 5-foot red-tailed boa captured in an East Main Street attic and in foundering health. That slippery critter had been spied on rooftops a couple of times before several people combined to capture the snake.

For about 10 days, Schenck gave the boa he dubbed “Cuddles” antibiotics, shifting to high-potency vitamins. “I’ll probably breed it this spring,” Schenck said, stroking the brown and tan snake.

As for the alligator, state environmental police took it into custody Sunday right after its capture.

How did it get there and where is it headed? Tom French, state Division of Fisheries and Wildlife assistant director, had answers to both questions.

Early Monday afternoon, French said he received a phone call from a young Tiverton man who claims to be the owner.

He said the man said he bought the alligator six years ago, and it had escaped during the past two weeks.

“He wanted us to give it back to him today, and we said no,” French said.

The issue of Rhode Island allowing alligators as pets has been “a pervasive source of aggravation for us,” he said. “We’ve taken the position that it’s not appropriate to keep alligators as pets.”

French said the man, whom he did not identify, said he planned to appeal the state’s position.

He said the Division of Fisheries and Wildlife handles an average of 50 captured alligators a year. Typically, people buy 8-inch hatchlings, keep them a few years and let them into the wild a few years later when, at about 3 feet long, they get too big.

“I want the public to know that alligators and poisonous snakes are not legal,” he said.

To handle animals people once kept as pets, such as monkeys, monitor lizards and alligators, French said, “I have a variety of people willing to hold things for me temporarily.” If he can find an educational center or zoo-type place with permits for that purpose close by, he said the animals are kept there permanently. In other cases, an alligator would be transported to Florida and put in a farm environment.

“We’ve never killed an alligator we’ve had in 25 years,” said French, who’s worked for the department that long.